I was able to reproduce that issue on our test servers and our developers will try to fix it as soon as possible.
As a temporary solution, I recommend you to switch popup theme in your gallery to 6 or 8: http://prntscr.com/i72lum
Option “Display only first image” should work properly with that themes.

hello, I’m having the same problem.
Show only first image dosen’t work: on click it opens the popup but shows only one image.
Tried also with enabling “Open by link in popup” but if in the page I link a text (for example text) and I put also the code [supsystic-gallery id=4]: in this case I can see the text linked (if click on it nothing happens) and under the text all the images of the gallery displaied in one column (if I click on one image it opens the popup and works fine)
Hope you can help me to fix this issue because I’m online with my client’s web site.
Thank you,
Cristian